Replacing Altech ALTHC001 Controller with Nest 3rd Gen

[ianmcd]

The neutral at the nest comes out of the boiler (with live, earth and a grey wire I guess is live return

post a pic of this wiring in the boiler

 

[agwright99]

post a pic of this wiring in the boiler

I will need to open up the boiler later to check but attached is the diagram in the manual which I’m basing my understanding on

 

[ianmcd]

I know what the wiring diagram looks like , I need to see what is in there

 

[agwright99]

I know what the wiring diagram looks like , I need to see what is in there

Ok attached.
Mains supply goes into a 3amp socket in the wall next to the boiler.
The LR, LS and NR go into the wall, with the LR and NR forming live and neutral in the controller and the LS joining the red wire up to the circuit box.

 

[agwright99]

This is odd - having re assembled the boiler the nest now seems to be operating the boiler as expected - ie I put the nest on manual and the boiler fires as you would expect. I will test some more and report back later... it could just be doing a “reboot” cycle and coincidence

 

[ianmcd]

More likely you have a loose connection somewhere

 

[agwright99]

More likely you have a loose connection somewhere

Morning - the boiler firing was a coincidence- it was running some sort of start up program (picture attached).
However that’s not to say I don’t have a loose connection so will go round and check everything again this morning.

 

[agwright99]

More likely you have a loose connection somewhere

So I’ve checked all the connections again this morning and I can’t find anything obvious. Running out of ideas. Is there a way to test other components of the system - eg the hot tank thermostat? The valve might be working but is missing a neutral supply - any possibility other than bad connection?
Edit: @stem fresh eyes here might help? Many thanks both in advance

 

[ianmcd]

The valve might be working but is missing a neutral supply

The valve wont do anything untill it gets a neutral supply, there is no neutral in the cyl stat so leave that alone, every time you turn the power off and back on to your boiler the boiler will run for a short time in syphon re-fill mode, only thing we havent looked at post a pic of the wiring behind the fused spur

 

[stem]

So as I see it:

1. You have tested with a multimeter between the motorised valve's white and blue wires when the Nest has the central heating switched 'on' and is calling for heat. The result is 0V
2. You have tested with a multimeter between the motorised valve's white and earth wires when the Nest has the central heating switched 'on' and is calling for heat. The result is 230V

As @ianmcd pointed out, that shows that the Nest is providing a live supply to the motorised valve, so the Nest is good. However the neutral is missing. Therefore you need to trace the neutral wire from the motorised valve back and find out where the connection has failed.

If the 'spare' blue wire behind the Altech was not connected to anything before when the system was working it won't be the neutral. The fact that it is 'live' worries me and should be investigated. For now at least insulate it and tuck it safely out of the way.

There are several blue wires at the Altech, two connected to it and one not. Is there any possibility that you have got them mixed up when you transferred them to the Nest? That 'spare' wire certainly looks as if it has been connected to something at sometime.

Would you be able to tell us what is actually connected to the other end of each of the 3 blue wires?

Edit.
@ianmcd replied whilst I was typing.

 

[stem]

In fact. On closer inspection.....Spot the difference in your before and after photographs. To make it easier, I've highlighted it for you. If you look carefully, there appears to be a second blue wire in the N terminal in the first photo.....

......so before reconnecting it anywhere, you just have to sort out which blue is which. But don't guess, get it wrong and it could cause problems. You are probably going to have to trace them back to their origin.

 

[agwright99]

In fact. On closer inspection.....Spot the difference in your before and after photographs. To make it easier, I've highlighted it for you. If you look carefully, there appears to be a second blue wire in the N terminal in the first photo.....

View attachment 221294

......so before reconnecting it anywhere, you just have to sort out which blue is which.

Well blow me down this seems to have worked... loose wire seems to be the missing neutral and needed to join the neutral going into the nest...
Just going to test it a few times and will report back.

 

[ianmcd]

Remember when you put the power back on you will have a delay untill the backward rugby posts dissapear on the display before the rads will start to heat up

 

[agwright99]

Both - thanks very much for your help pleased to say all now operating correctly. I will buy you a virtual pint

needs a fair bit of tidy up and link off the old thermostat in the circuit box - will post in a few days once I’ve sorted.

thanks again

 

[stem]

"The Devil is in the detail"